It is known to equip motor vehicle transmissions such as automatic or dual-clutch transmissions with a parking lock, in order to prevent the vehicle from rolling away. The structure of such a parking lock is described, for example, in DE 199 33 618 A1 by the present applicant: a locking pawl is mounted on the transmission housing by means of a bolt, the so-termed parking lock bolt, and loaded by a restoring spring, for example a lever spring, in the circumferential or swiveling direction. The locking pawl comprise a pawl tooth which engages in a tooth gap on a parking lock gear arranged on the transmission output and blocks it, i.e. so that the parking lock is engaged. The known parking lock device also comprises a guide plate supported on the housing and serving as the abutment for a locking cone, which locks the locking pawl in its engaged condition. The locking cone is actuated by a connecting rod. When the locking cone is retracted the locking pawl is released and swiveled back by the restoring spring, so that the pawl tooth disengages from the parking lock gear—and the parking lock is then in its disengaged condition.
From DE 102 45 951 A1 a parking lock device has become known, which has at its free end a so-termed pawl hook which is guided in a guide slot of the guide plate.
A problem that occurs in the disengaged condition of the parking lock, for example when driving on roads in poor condition or with marked vibrations of the transmission, is that the locking pawl can become loose on the guide plate—against the force of the restoring spring—and tooth-crown contact can take place between the pawl tooth and the parking lock teeth. This can result in damage to the parking lock system.
To solve this problem various approaches have already been tried, for example as in DE 10 2006 022 963 A1, where a hydraulically actuated locking device is provided to hold the locking pawl steady in its disengaged condition.
From EP 0 895 908 A1 a parking lock device with a locking pawl is known, which in its disengaged condition is locked by an electromagnetically actuated locking bolt. Both of these previously known solutions have the disadvantage that additional components are required for the locking device, and this increases the structural complexity, the weight and the cost of the transmission.
In the older application by the present applicant with file number DE 10 2008 054 467.1 a parking lock device with a locking pawl is disclosed, which in its disengaged condition is secured with positive interlock by a moveable securing element by means of a spring element.